X-ray image intensifier screen



April 24, 1956 R. L. I ONGINI X-RAY IMAGE INTENSIFIER SCREEN Filed March 29, 1952 Fig. l.

INVENToR Richard L. Longini.

WITNESSES:

wq ff/f {4Q/WM y United States Patent() X-RAY IMAGE INTENSIEIER SCREEN Richard L. Longini, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a cor- .porationv of. Pennsylvania Application March 29, 1.952, lserial No. 279,414

1s claims'. (ci. 117-211) My yinvention relates to fluorescent screens, and in particular relates to an arrangement for eliminating the slow decay component of light which is characteristic `of certain such screens .as zinc sulphide-silver.

Zinc sulphide-silver has many highly desirable qualities for lluorescent screens such as those used in X-ray fluoroscopy and in particular has provedhighly satisfactory in many respects for the uorescent material used in the X-ray Image intensifier described in Mason and Coltman U. S. Patent 2,523,132. However it has been found to have one somewhat undesirable characteristic in the form of a slow building up of energy storage during X-radiation, which stored energy is later ygiven out as an afterglow continuing for hours after the X-radiation has ceased. In the course of several hours use for X-ray examination this accumulated-after glow becomes strong enough to partially obscure picture detail.

`In accordance with my invention I avoid the above which zinc sulphide (silver) -emits under incidence 'of X-rays or electrons. Superpesed onk the layer 'Z-zis a layer 3 of zinc sulphide-silver or other .phosphor having an undesired emissive` component, the emission of which is expedited by light of ther character given out by .the layer 2. To give a specific example theglass backingplate 1 may be about 15 cm. `in diameter by 0.1 cm.k thick; the layer 2 may be of ZnS(Mn) about 002cm. thick; andthe layer 3 may be 0.01 cm. thick.

. When X-rays lare projected through the ,backing-layer 1 some are `absorbed in layer, 2 `but a greater portion passes through and may be' absorbed by the layer 3. AThe portion absorbed in layer 2 generates red vlight a large portion of which is absorbed in. layer 3,.- an'd there prevents the long-time. storage of the energyI which theX-ra'ys would other'wise buildup in layer 3 producing alongterm afterglow.` f

. The screen of Fig. 1 may be employed in the X-ray image intensilier of Fig. 2 which comprises a vacuummentioned persistent afterglow by providing a layer of light partly by the incident X-rays vor other primary radiation anti` partly by the bluish radiation generated by that primary radiationy in the zinc sulphide-silver. Such red light has the effect of releasing l,the above-mentioned slowly stored energy from the zinc sulphide-silver. One suitable red-emitting phosphor is zinc sulphide-manganese, ZnS(Mn) but other substances whichfemit red or even infra-red radiation may also 'be used.

One object of my invention isy to provide means for eliminating the afterglow just described in zinc sulphidesilver and other fluorescentmaterials showing it.

Another object ofmy invention is to provide a novel type of fluorescent screen.

Still another object is to provide a short-persistence iiuorescent screen of high etnciency inv transforming X- raysy into light.y

Another object. is to provide a composite uorescent screen having the short-time luminous characteristics, of zinc sulphide-silver screen without the long-time afterglow foundy in the latter.-

A further object is to provide any improved form of n image intensifier free from substantial cumulative long term background glow.

Other objects-of-my yinvention will become evident on reading the following description taken in connection with the drawings irl-which: y

Fig 1 shows aflluorescent screen embodying the principles of my invention; and f 'i Fig. 2 shows an image intensifier. tubeemploying vsuch a screen. w

Referring to the drawings in detail the fluorescent screen of Fig. l comprises a glass backing-layer 1, which may for example have the shape of a watch-glass, of lime-glass having a layer 2 of a phosphor such asv zinc sulphide-manganese [ZnS(MN)] which emits red orinfra-red light (i. e. light not lower than 6000 angstroms in wave length) when irradiated with the bluish light tight envelopeI 17 which has a transparent end portion 19 near which the fluorescent screen of Fig. rl is mounted.V

On the input uorescent surface, a transparent conductive layer 25 is deposited. A suitable transparent conductoris manufactured b y the Pittsburgh lPlate Glass Company and is identified? by vthe1trade-naruel Nesa.

A photosensitive surface `27 is formed on the transparent conductive layer 25. This -photosensi'tive surface should have the property of emittingl electrons substantially only when lighty ofA the frequencies equal to` or greater than that ofthe: light emitted bythe input fluorescent screen impinge thereon. In` the vpreferred, practice of the invention, the photosensitive screen is` composed of cesium-antimony.v In the following specification I shall refer to his photo-electric surface as of theA caesium antimony type.

The transparent barrier 25 between Vthe input fluorescent screen 3 and the photoelectric surface 27 is used to assure a conductive return for the; charges which. leave the photoelectric surface during. operation. This conductive barrier isv necessitated by the fact that in general the photosensitive surface 271is not sufficiently conductive'to serve asa return. .111 certainr` situations, the photosensitive material may be A.sufficiently conductive. In such situations, the transparent layer 25 may be. nonconductive or omitted; .for example, it lmay be glass' of the type with which 'the `fluorescent .material of the input screen 3 is mixed. i f

A plurality of. conductive cylinders 29,31,`33, 35 and 37y of progressively increasing lengthl and .progressively decreasing `diameter extend Vfromthe'i'nput plate longitudinally along the envelope 1'7. Theiir'st of these cylinders 29 is insulated from vthe input plate andv each of the other cylinders is insulated from succeeding and preceding cylinders. y Potentials of different magnitudesare impressed on the cylinders 29 to 37 from a suitable voltage, divider 39. The cylinders function asv an electron optical lens system for the electron image emitted by the photosensitive surface 27.l ,y

The cylinder 37 having the smallest diameter lextends into a constricted neck 41 ofy the envelope vv17. Atthe terminal of this neck, very nearto the opening of the cylinder 37 of smallest diameter, the composite output fluorescent plate 13 is-moun'ted. This compositeplatecis composed ofv an electron-responsive,phosphor screen on which a layer of aluminum is deposited. The phosphor may be of any suitable type but in accordance with the preferred practice of our invention is composed of zinc cadmium sulphide and is identified by RCA Victor, its manufacturer, as 33Z604B. The aluminum layer is of sufiicient thickness to obstruct back emission of light from the output phosphor to the photosensitive surface 27 and sufficiently thin to permit penetration of the electrons.

While I have described the zinc sulphide-silver and zinc sulphide-manganese as if in separate layers they may be mixed to form a single layer;

I claim as my invention:

1. A fluorescent screen comprising a layer of zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising cesiated antimony and an electrically conductive material transparent to the fluorescent light from said zinc sulphide-silver, and supporting means for said layer. t

2` A fluorescent screen comprisingv a ylayer of zinc sulphide-silver and a material which emits radiation predominantly above 6000 angstroms in wave-length when irradiated by the fluorescent `light of said zinc sulphidesilver, a coating comprising an electrically-conductive first material which is transparent to the fluorescent light of said zinc-sulphide-silver and a photoelectric second material which emits electrons when struck by said fluorescent light and being superposed on said layer, and supporting means which is transparent to X-rays on the opposite side of said coating from said layer.

3. `A fluorescent screen comprising a layer of zinc sulphide-silver and a material which emits radiation predominantly above 6000 angstroms in wave-length when irradiated bythe fluorescent light of said zinc sulphidesilver, a coating comprising cesiated antimony and an electrically-conductive material which is transparent to the fluorescent light of said zinc sulphide-silver superposed on said layer, and supporting means for said layer.

4. A fluorescent screen comprising a layer of zinc sulphide-silver and a first material which emits radiation predominantly above 6000 angstroms in wave-length when irradiated by radiation which is below 6000 angstroms in wave-length, a coating on said layer comprising an electrically conductive second material which is transparent to the fluorescentllight of said zinc sulphide-silver and a photoelectric third material which emits electrons when struck by said light, and supporting `means which is transparent to X-rays-on the opposite side of said coating from said layer.

5. Afluorescent screen comprising a layer of zinc sulphide-silver and a material which emits radiation predominantly above 6000 angstroms in wave-length when irradiated by radiation which is below 6000 angstroms in wave-length, .a coating on said layer comprising cesiated antimony and an electrically conductive material which is transparent to the fluorescent light of said zinc sulphide-silver, and supporting means for said layer.

6. A fluorescent screen comprising a layer comprising zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising an electrically conductive material which is transparent to the fluorescent light of said zinc sulphide-silver, and a photoelectric material which emits electrons whenstruck by said light, and supporting means for said layer.

7. A lluorescent screen comprising a layer comprising zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising cesiated antimony and an electrically conductive material which is transparent to the fluorescent light of said zinc sulphide-silver, and supporting means on the opposite side of said coating from said layer. L

8. An X-ray image intensifier comprising a fluorescent screen comprising a layer of zinesulphide-silver and a first material which emits radiation of wave-length predominantly greater than 6000 angstroms when irradiated by the fluorescent light from said zinc sulphide-silver, a

coating on said layer which comprises an electrically conductive second material which is transparent to the fluorescent light of said zinc sulphide-silver and a photoelectric third material which emits electrons when struck by said light, supporting means for said layer, and an output screen upon which said electrons are incident.

9. An X-ray image intensifiercomprising a fluorescent screen comprising a layer of zinc sulphide-silver and a first material which emits radiation of wave-length predominantly greater than 6000 angstroms when irradiated by the fluorescent light from said zinc sulphide-silver, a coating on said layer which comprises cesiated antimony and an electrically conductive second material which is transparent'to the fluorescent light of said zinc sulphidesilver, supporting means for said layer, and an output screen upon which said electrons are incident,

l0. An X-ray image intensifier comprising a layer of zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising an electrically conductive material which is transparent to the fluorescent light of said zinc sulphide-silver and a photoelectric material which emits electrons when struck by said light, supporting means for said layer, and an output screen to receive said electrons.

ll. An X-ray image intensifier comprising a layer of Zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising cesiated antimony which emits `electrons when struck by the output light from said layer when said layer is energized by X-rays, and an electrically conductive materialv which is transparent to the fluorescent light of said zinc sulphide-silver, supporting means for said layer, and an output screen to receive said electrons.

l2. A fluorescent screen comprising a layer of zinc sulphide-silver and zinc sulphide-manganese, a coating on said layer comprising an electrically conductive first material transparent to the fluorescent light from said zinc sulphide-silver and a photoelectric second material which emits electrons when struck by said light, and supporting means transparent to X-rays and positioned on the opposite side of said coating from said layer.

l3. A ffuoroscopic device adapted for operation with a source of a radiant energy image and an output screen, said device comprising a first layer of zinc sulphide-silver, a second layer on said first layer and comprising zinc sulphide-manganese, each `of said first and second layers being operative to emit light when energized by radiant energy from said source, a third layer on the second layer and comprising a photoelectric material which emits electronswhen struck by said light, support means including a fourth layer positioned on the third layer and comprising a material transparent to said radiant energy, said device being adapted for operation with said source such that all of said layers may be positioned between the source and the output screen, with the fourth layer positioned closest to the source and the first layer positioned closest to the screen.

References Cited in the le of this patent UNITED STATES PATENTS 2,185,439 Hinderer Ian. 2, 1940 2,360,516 Schmidling Oct. 17, 1944 2,403,227 Leverenz July 2, 1946 2,447,322 Fonda Aug. 17, 1948 2,476,619 Nicoll Iuly 19, 1949 2,504,674 Fonda Apr. 18, 1950 2,523,132 Mason et al Sept. 19, 1950 

8. AN X-RAY IMAGE INTENSIFIER COMPRISING A FLUORESCENT SCREEN COMPRISING A LAYER OF ZINC SULPHIDE-SILVER AND A FIRST MATERIAL WHICH EMITS RADIATION OF WAVE-LENGTH PREDOMINANTLY GREATER THAN 6000 ANGSTROMS WHEN IRRADIATED BY THE FLUORESCENT LIGHT FROM SAID ZINC SULPHIDE-SILVER, A COATING ON SAID LAYER WHICH COMPRISES AN ELECTRICALLY CONDUCTIVE SECOND MATERIAL WHICH IS TRANSPARENT TO THE FLUORESCENT LIGHT OF SAID ZINC SULPHIDE-SILVER AND A PHOTOELECTRIC THIRD MATERIAL WHICH EMITS ELECTRONS WHEN STRUCK BY SAID LIGHT, SUPPORTING MEANS FOR SAID LAYER, AND AN OUTPUT SCREEN UPON WHICH SAID ELECTRONS ARE INCIDENT. 